Field of the Invention
This invention relates to illumination and display fields, and in particular, it relates to a display uniformity compensation method, an optical modulation device, a signal processor, and a projection system.
Description of Related Art
Projection devices are widely used in cinemas, meetings, advertisement and other application fields. Optical modulation techniques in projection devices are generally divided into three light valve modulation and single light valve modulation techniques. A typical projection system using single light valve modulation includes a red light source, a green light source and a blue light sources for respectively generate a red (R) light, a green (G) light and a blue (B) light, and a light valve for modulating the red, green and blue lights to generate a light beam representing a color image, and a projection lens for projecting the light beam of the color image which has been modulation by the light valve on a screen to produce a color image. The red, green and blue light beams may be (but without limitation) guided by reflectors to a light combining prism, and the combined light is output to the light valve. The light valve may be a MEMS (micro-electro-mechanical system) device, such as a light valve using digital light processing (DLP) technology provided by Texas Instrument.
The signal processor receives at least on frame of image signal, converts it to image data, and outputs the image data to the light valve; meanwhile, it controls the respective light sources and the light valve by their drive signals, so that the light valve modulates the corresponding color light beams based on the received image data. For example, when the signal processor sends the red image data of a frame of image data to the light valve, the red light source is turned on to emit red light; similarly, when the signal processor sends the green or blue image data of a frame of image data to the light valve, the green or blue light source is turned on to emit green or blue light. When the signal processor sends white/gray image data of a frame of image data to the light valve, all of the red, green and blue light sources are turned on.
This way, using a light valve to modulate a color light sequence of rapid periodically repeating red, green and blue monochromatic lights, a corresponding periodically repeating red, green and blue primary color image sequence is obtained; the primary color image sequence is projected onto a screen by projection lenses. As long as the speed of change of the image sequence is sufficiently fast, human eyes cannot distinguish individual primary color images, and the three primary color images are combined into a moving image due to the persistence of vision of human eyes.
In a projection display system that uses the three light valve modulation technique, three light valves are used to respectively modulate the red, green and blue primary colors, to generate monochromatic images of each primary color. The monochromatic images are then combined into a color image using dichroic filters or other light combining devices, and projected onto a screen by a projection lens.
Regardless of the type of projection devices, all lights are modulated by light valves and then projected on to the screen by projection lenses. However, when the light modulated by the light valve is transmitted through the projection lenses, large angle lights often experience losses, so the brightness of the image in the four corner regions of the screen is typically lower than that in the center region. This is troublesome for many application. For example, when multiple display units are pieced together to form a display wall, the above problem will cause inconsistent brightness and color of the display wall, so that the display has a patchy appearance, affecting the visual effect.
One commonly used solution to the above problem is to process the input signal, to lower the grayscale values in the center region of the display unit to reduce the image brightness of the center region of the display unit, thereby improving the uniformity of each display unit. When piecing the units together, the brightness of each of the multiple display units is adjusted based on the brightness of the least bright display unit, to achieve consistency of the entire display wall. However, this solution reduces the dynamic range of the display.